According to U.S. Government statistics, only about one-third of American fourth-graders are reading at a proficient level. Fourth grade is a pivotal year in elementary school as the curriculum typically requires students to shift from learning the basics of how to read to using established reading skills in an adult-like manner, to gain and build new knowledge. Behavioral data suggest that context-free recognition of simple, high frequency words is automatic by the fourth grade in typically developing readers but neural data are scarce. The proposed research with groups of third-, fourth-, and fifth-graders uses both standardized behavioral measures of various reading skills (orthographic, phonological, semantic, and comprehension) and a measure of neural word processing, the N400 component of the event-related potential (ERP) waveform. In previous studies with adults, the N400 has been shown to index both lexicosemantic and higher-level aspects of word processing. Here, the N400 will be recorded to simple real words (e.g., bed), pseudowords (e.g., bem), nonpronounceable letter strings (e.g., mbe), and strings of letter-like stimuli (e.g., BEM) presented in list form. It is predicted that only orthographically and phonologically legal stimuli (words and pseudowords) will elicit an N400 in older children/better readers, while all types of stimuli may elicit an N400 in younger children/poorer readers who have not yet automatized lower-level processes related to reading;consistent with this, correlations between the brain and behavioral measures are predicted to change over developmental time. This pattern of findings would indicate a neurocognitive word processing system that is more open to linguistic possibility and less selective in processing strings as word candidates in younger children/poorer readers, showing that some children in late elementary school indeed may not yet be processing word and word-like stimuli similarly to adults. Such insights might have implications for teaching and learning in the classroom, particularly for the many children at risk and struggling to read in late elementary school. In a broad, long-term view, such investigations of word-level processing using both neural and behavioral measures in children and adults will provide converging and constraining evidence that will lead to a better, multilevel understanding of the development of word processing systems that are at the core of reading skills. PUBLIC HEALTH RELEVANCE: Children who are poor readers are at risk for disengagement from school and eventual school failure, leading to other public health risks. Basic research that investigates the development of word reading skills in terms of both brain and behavior, as proposed here, can lead to a better understanding of the developmental course of reading skills. Such scientific advances in understanding can eventually be used in the classroom for better teaching and learning, and for design of remediation programs for poor readers.